1. Field of the Invention
The present invention relates to a combustor dome assembly for a gas turbine engine, and, more particularly, to an integral cowl plate/ferrule retainer for such combustor dome.
2. Description of Related Art
One of the critical parameters in combustor design is regulating the amount of air flow entering the dome assembly. This involves matching the "capture area," or area across the entrance of the combustor dome which is open to flow, to the diffuser opening (generally a ratio of approximately 3:1). The capture area is sized through the implementation of certain blockage elements such as cowls. If the capture area is not properly sized, it may cause spillage or regurgitation of air away from the dome (capture area too large) or reduce efficiency from the lack of air (capture area too small).
Current gas turbine engine combustors have generally been of a single annular design, whereby they contain one circumferential row of air swirlers and fuel nozzles. Annular inner and outer cowls are provided to define the inlet area to the combustor dome for the flow of air from the engine compressor. Accordingly, the inner and outer cowls provide the required capture area for high pressure recovery into the dome. In order to maintain an appropriate interface between the fuel nozzle and the swirl cup, a floating ferrule is provided and retained in the swirl cup casting by a sheet metal retainer.
More recently, dual annular combustors containing two rows of circumferential air swirlers and fuel nozzles have been developed. Such designs provide similar combustion performance to single annular combustors in essentially half the length thereof. However, the dual annular combustor requires less capture area (or more dome blockage) than two cowls can provide because of the increased dome height. Otherwise, spillage of the air from the dome region into the inner or outer passages of the combustor occurs, resulting in significant total pressure losses. Therefore, a total of four cowls are normally used in dual annular designs to provide the required capture area/blockage for each of the domes. This translates into inner and outer cowls being provided for each dome (four cowl design). In this design, air not captured by the two pairs of cowls is directed into a centerbody or the outer or inner passages. Existing dual annular designs, such as that disclosed in a development report to NASA for the Energy Efficient Engine (E.sup.3), consist of separate inner and outer domes separated by a centerbody and bolted to two sets of inner and outer cowls. In this design, stamped sheet metal ferrule retainers are utilized.
It has been found that if a single continuous dome plate could be utilized, the centerbodies of prior art dual annular combustors could be eliminated, resulting in the advantages of reduced cost and weight, reduced cooling flow, and enhanced cross-fire between the domes. When the four-cowl configuration discussed above has been implemented in this design, however, attachment of the two center (or mid-dome) cowls has been extremely difficult. Moreover, the four-cowl design has no pressure communication between the domes and is therefore more sensitive to exit velocity profile fluctuations out of the diffuser.
Accordingly, a primary objective of the present invention is to provide a dual annular combustor having a single continuous dome plate with adequate dome blockage and pressure recovery.
Another objective of the present invention is to provide a dual annular combustor dome assembly having a single continuous dome plate with a two-cowl design.
Yet another objective of the present invention is to reduce the amount of weight of the combustor dome structure.
These objectives and other features of the present invention will become more readily apparent upon reference to the following description when taken in conjunction with the following drawing.